Researchers at the School of Veterinary Medicine and Perelman School of Medicine have discovered that pro-B cells lacking YY1 can develop into T lineage cells, which assist B cells in forming antibodies.
B cells, crucial white blood cells that produce antibodies, go through several stages during their development: from common lymphoid progenitors to pre-pro-B cells, pro-B cells, pre-B cells, and then immature B cells, eventually becoming more mature and specialized B cells. At the pro-B stage, these cells are typically destined to remain as B cells and not differentiate into other types.
However, according to the researchers from the School of Veterinary Medicine and Perelman School of Medicine, the absence of YY1 in pro-B cells disrupts their commitment to the B cell lineage, allowing for unexpected flexibility in blood cell development. YY1 is a widespread transcription factor that can both activate and suppress gene expression and is crucial for various cellular processes, including cell growth, DNA repair, and embryonic development.
The team discovered that pro-B cells without YY1 can produce T lineage cells, which help B cells in antibody production, in laboratory settings and mouse models. Their research has been published in the journal Genes & Development.
“The results exceeded my greatest expectations,” said senior author Michael Atchison, a professor of biomedical sciences at Penn Vet. He emphasizes the significance of YY1, stating, “Its universal expression across various lineages suggests a strong potential for regenerative medicine.”
He envisions a scenario where YY1 could be temporarily silenced, redirected toward a different cell type, and then reinstated, potentially reintroducing muscle cells into patients suffering from muscle diseases.
“While other transcription factors associated with specific lineages have shown some flexibility in B cell development, YY1 is unique because it is universally expressed in all cell types, highlighting a possible universal mechanism for lineage commitment,” the authors note.
Atchison recalls that early in his tenure at Penn Vet, around 1989, one of his graduate students successfully cloned YY1. This was a groundbreaking time, as it was surprising to learn that a transcription factor could activate some genes while repressing others. Over 30 years ago, multiple laboratories made similar findings, leading to the naming of the transcription factor Yin Yang 1 due to its dual roles.
The foundation for this paper was laid nearly ten years ago by a former postdoctoral researcher who, analyzing RNA sequencing data, speculated that pro-B cells lacking YY1 could transition into T cells. Sarmistha Banerjee, the paper’s first author, later continued this research as a senior research investigator at Penn.
The researchers utilized a technique to eliminate YY1 using Mb1-driven CRE, where CRE is a protein that can remove DNA, and Mb1 directs the expression of CRE in pro-B cells.
“We anticipated a gradual shift from B to T cells, but during this process, we noticed several unexpected gene expressions in the resulting mature T cells,” Atchison explains. Collaborator Joshua Rhoades, a bioinformatician, suggested performing single-cell RNA sequencing, which Atchison says “proved to be transformative, revealing the emergence of multiple other cell types.”
The sequencing results indicated that as YY1 knockout pro-B cells matured in culture, 85% identified as monocytic or dendritic cells, which play a role in antigen presentation to activate B and T cells, while only 3% were recognized as T cells. Notably, after three weeks of incubation, there was a significant downregulation of alternative lineage genes and an increased expression of T lineage genes.
“An insightful and surprising finding was that while we directed these B cells toward becoming T cells in the right T cell environment, we found they were also forming various other cell types midway through the transition,” states co-author Sarah Naiyer, a research associate in immunology at Penn. She mentions that “Notch, a receptor in a well-conserved cell signaling pathway, played a critical role in this development, indicating that the gradient of Notch signaling is vital for generating other cell types initially while restraining their differentiation later, guiding them toward T cell maturation.”
Atchison expressed his satisfaction with seeing these preliminary results replicated in live models. “The findings align closely with our initial predictions on how the genome alters when YY1 is knocked out, contributing to a lesser commitment to a single lineage that permits transition into another type,” he remarks.
Looking ahead, the extensive data collected by the team “can be explored further to understand the implications of YY1 knockout,” according to Atchison. “We have examined a limited number of genes, while there are about 20,000 genes in the genome, leaving substantial opportunities for further research with our current data.”
Future research directions include investigating the effects of YY1 knockout across other cell types and tissues, and exploring whether T cells can transition into other lineages.
Michael Atchison is a professor in the Department of Biomedical Sciences, director of the VMD-Ph.D. Program, and director of the NIH/Boehringer-Ingelheim Summer Research Program at the University of Pennsylvania School of Veterinary Medicine.
Sarmistha Banerjee previously conducted research in the Atchison Lab at Penn Vet.
Sarah Naiyer is a research associate specializing in immunology at Penn Vet.
Joshua Rhoades works as a bioinformatician at Penn Vet.
Additional co-authors include Penn Vet’s Nasreen Bano, Dawei Dong, Suchita Hodawadekar, and Sulagna Sanyal; along with David Allman and Anupam Banerjee from the Department of Pathology and Laboratory Medicine at Perelman School of Medicine.
This research was funded by the National Institutes of Health (grants R01AI162879, R01AI155540, R01AI139123, and R01AI175185), alongside an Aspire award from the Mark Foundation for Cancer Research.
